GPU: Switched from constant preprocessor defines to constexpr in namespaces to prevent naming conflicts.

See merge request irmb/VirtualFluids_dev!46

# Conflicts:
#	CMake/VirtualFluidsMacros.cmake
#	CMakeLists.txt
#	src/cpu/VirtualFluidsCore/CoProcessors/MPIIOMigrationBECoProcessor.cpp
#	src/cpu/VirtualFluidsCore/CoProcessors/MPIIOMigrationCoProcessor.cpp
#	src/cpu/VirtualFluidsCore/CoProcessors/MPIIORestartCoProcessor.cpp
#	src/gpu/VirtualFluids_GPU/CMakeLists.txt
#	src/gpu/VirtualFluids_GPU/LBM/Simulation.cpp

Fixes warnings in develop

See merge request irmb/VirtualFluids_dev!45

MultiphaseVelocityBCAlgorithm::applyBC(): vleocity in phase field taken from...

See merge request irmb/VirtualFluids_dev!44

Classical rescaling of phase field distribution to 1/3 rho as common in Lee-literature. The source terms were removed from the moments and returned to the distributions based on the original code of Safari.

Remove boost serialization and fix the seg fault issue.

See merge request irmb/VirtualFluids_dev!43

add body force arrays is three dimensions for hole domain

See merge request irmb/VirtualFluids_dev!42